I've had this happen occasionally. I've been binding daily for about 3.5 years now, and the inverted nipple thing started happening about 2 years ago. Generally I don't worry about it. I looked it up online, and having an inverted nipple seems to be a fairly common thing for both men and women. I had one time where it was inverted and oozing this sticky fluid, and I kind of freaked out about that for a while, but it only happened once and it was kind of a long time ago. But if it's something that concerns you, maybe bring it up with your doctor the next time you see them? I'm a bad person to give advice on this sort of thing, because I don't take care of my health the way I should, especially with respect to my more feminine body parts. But yeah, it can't hurt to ask your doctor, if that's something you're comfortable with.